Species interactions and random dispersal rather than habitat filtering 1 drive community assembly during early plant succession

31 Theory on plant succession predicts a temporal increase in the complexity of spatial 32 community structure and of competitive interactions: initially random occurrences of early 33 colonising species shift towards spatially and competitively structured plant associations in 34 late successional stages. Here we use long-term data on early plant succession in a German 35 post mining area to disentangle the importance of random colonisation, habitat filtering, and 36 competition on the temporal and spatial development of plant community structure. We used 37 species co-occurrence analysis and a recently developed method for assessing competitive 38 strength and hierarchies (transitive versus intransitive competitive orders) in multispecies 39 communities. We found that species turnover decreased through time within interaction 40 neighbourhoods, but increased through time outside interaction neighbourhoods. Successional 41 change did not lead to modular community structure. After accounting for species richness 42 effects, the strength of competitive interactions and the proportion of transitive competitive 43 hierarchies increased through time. Although effects of habitat filtering were weak, random 44 colonization and subsequent competitive interactions had strong effects on community 45 structure. Because competitive strength and transitivity were poorly correlated with soil 46 characteristics, there was little evidence for context dependent competitive strength associated 47 with intransitive competitive hierarchies. 48 49 Running title: Plant community structure in early plant succession 50 51